A variety of electroplating baths have been disclosed for the electrodeposition of bright tin upon metallic substrates. These baths have been substantially acidic and have been utilized in many industrial applications. Typical of such disclosed baths include those described in U.S. Pat. Nos. 3,361,652; 3,471,379 and 3,875,029.
Many of these aforementioned baths contain surface active agents and the baths aforementioned typically contain a brightener. While these baths have proven generally satisfactory and have been widely utilized in a commercial setting, they are usually deficient in one or more desirable operating characteristics, and the deposits produced thereby frequently fail to provide a balance of characteristics such as smoothness, brightness, adherence, solderability and stability to resist aging, particularly in the presence of copper ions present as contaminants in the acid plating baths.
Therefore, while various of the baths described in the literature are operable with varying degrees of effectiveness, there has remained a need to provide a means for treating a copper-contaminated bath to produce a bath which is again capable of producing smooth adherent deposits exhibiting spectral brightness over a wide current density range.
It has now been determined that by utilizing sodium formaldehyde sulfoxylate as an additive, a copper-contaminated acid tin or tin-metal alloy electroplating bath can be treated to regenerate a bath which is substantially stable and is capable of producing bright, smooth, fine-grained deposits over a wide cathode current density range upon continued electrolysis.